U.S. patent application number 11/230282 was filed with the patent office on 2006-03-23 for lithium secondary battery.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Kenshin Kitoh, Tsutomu Mori, Shinji Ohtsubo, Wataru Shionoya.
Application Number | 20060063063 11/230282 |
Document ID | / |
Family ID | 36074435 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060063063 |
Kind Code |
A1 |
Mori; Tsutomu ; et
al. |
March 23, 2006 |
Lithium secondary battery
Abstract
A lithium secondary battery 1 including: an inner electrode
member 6 having electrode plates (cathode plate 2, anode plate 3)
of a metal foil as a constituting element, and being formed by
winding or laminating electrode plates; and a battery case 10 for
housing the inner electrode member 6. A gas release channel capable
of releasing a gas to the outside of the battery case 10 is formed
by deformation of the inner electrode member 6 by a function of a
raised inner pressure when the inner pressure of the battery case
10 rises to a predetermined pressure or more due to the gas
generated inside the inner electrode member 6. The lithium
secondary battery can smoothly release the gas generated inside the
inner electrode member without being retained therein before the
gas reaches a pressure releasing mechanism; thus, it is superior in
safety and has a high energy density.
Inventors: |
Mori; Tsutomu; (Handa-city,
JP) ; Shionoya; Wataru; (Nagoya-city, JP) ;
Ohtsubo; Shinji; (Nagoya-city, JP) ; Kitoh;
Kenshin; (Nagoya-city, JP) |
Correspondence
Address: |
BURR & BROWN
PO BOX 7068
SYRACUSE
NY
13261-7068
US
|
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
36074435 |
Appl. No.: |
11/230282 |
Filed: |
September 19, 2005 |
Current U.S.
Class: |
429/53 ; 429/61;
429/82; 429/94 |
Current CPC
Class: |
H01M 50/463 20210101;
H01M 10/0431 20130101; H01M 10/0525 20130101; H01M 50/35 20210101;
Y02T 10/70 20130101; Y02E 60/10 20130101; H01M 10/0587 20130101;
H01M 10/0585 20130101 |
Class at
Publication: |
429/053 ;
429/094; 429/082; 429/061 |
International
Class: |
H01M 2/12 20060101
H01M002/12 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2004 |
JP |
2004-274799 |
Jun 29, 2005 |
JP |
2005-189263 |
Claims
1. A lithium secondary battery comprising: an inner electrode
member having wound or laminated electrode plates of a metal foil;
and a battery case for housing the inner electrode member, wherein
when an inner pressure of the battery case rises to a predetermined
pressure or more by a gas generated inside the inner electrode
member, a gas release channel which allows the release of the gas
to the outside of the battery case is formed by deformation of the
inner electrode member by a raised inner pressure.
2. The lithium secondary battery according to claim 1, wherein at
least a part of the gas release channel is formed inside the inner
electrode member in a direction vertical to the surface of the
inner electrode member onto which the electrode plate is wound or
laminated.
3. The lithium secondary battery according to claim 2, wherein the
deformation indicates that a pre-designed predetermined portion of
the metal foil is broken to form a hole.
4. The lithium secondary battery according to claim 1, wherein the
inner electrode member further has a core member onto which the
electrode plate is wound or laminated.
5. The lithium secondary battery according to claim 4, wherein the
core member is shaped to have a predetermined inner space and one
or more through-holes formed to communicate with the inner space,
and the metal foil in the vicinity of the through-hole is broken to
form a hole, and the gas release channel is formed which allows the
release of the gas to the outside of the battery case through the
hole, the through-hole, and the inner space by the function of the
raised inner pressure in the case where the inner pressure rises to
the predetermined or more pressure.
6. The lithium secondary battery according to claim 4, wherein the
core member is provided with one or more groove portions which
extend to at least one end portion of the core member, and the
metal foil in the vicinity of the groove portion is broken to form
a hole, and the gas release channel is formed which allows the
release of the gas to the outside of the battery case through the
hole and the groove portion by the function of the raised inner
pressure in the case where the inner pressure rises to the
predetermined or more pressure.
7. The lithium secondary battery according to claim 4, wherein the
core member is provided with two or more core member elements
having hollow portions and disposed in such a manner that gap
portions having predetermined intervals are formed between the
respective core member elements and the hollow portions communicate
with each other, and the metal foil in the vicinity of the gap
portion is broken to form a hole, and the gas release channel is
formed which allows the release of the gas to the outside of the
battery case through the hole, the gap portion, and the hollow
portions by the function of the raised inner pressure in the case
where the inner pressure rises to the predetermined or more
pressure.
8. The lithium secondary battery according to claim 3, further
comprising: a first exterior member which is disposed between the
inner electrode member and the battery case and which has a
predetermined inner space and which is provided with one or more
through-holes which communicate with the inner space, wherein the
metal foil in the vicinity of the through-hole is broken to form a
hole, and the gas release channel is formed which allows the
release of the gas to the outside of the battery case through the
hole, the through-hole, and the inner space by the function of the
raised inner pressure in the case where the inner pressure rises to
the predetermined or more pressure.
9. The lithium secondary battery according to claim 3, wherein a
strength (F1) of the battery case against pressure and a strength
(F2) of the portion of the metal foil against pressure in which the
hole is formed satisfy a relation of F2<F1.
10. The lithium secondary battery according to claim 1, wherein the
inner electrode member is expanded and deformed in a thickness
direction of the electrode plate, a space portion is formed between
the electrode plates disposed adjacent to each other, and the gas
release channel is formed which allows the release of the gas to
the outside of the battery case through the space portion by the
function of the raised inner pressure in the case where the inner
pressure rises to the predetermined or more pressure.
11. The lithium secondary battery according to claim 10, further
comprising: a second exterior member which is disposed between the
inner electrode member and the battery case and which is deformable
at a predetermined pressure, wherein the second exterior member is
deformed, and the inner electrode member is expanded and deformed
in a thickness direction of the electrode plate by a function of
the raised inner pressure in the case where the inner pressure
rises to the predetermined or more pressure.
12. The lithium secondary battery according to claim 1, wherein the
battery case comprises a pressure releasing mechanism, and an end
of the gas release channel communicates with the pressure releasing
mechanism.
13. The lithium secondary battery according to claim 1, wherein a
shape of the core member is a pipe-shape, and a whole shape of the
battery is cylindrical.
14. The lithium secondary battery according to claim 1, wherein a
shape of the core member is a hollow plate-shape, and a whole shape
of the battery is prismatic.
Description
TECHNICAL FIELD
[0001] The present invention relates to a lithium secondary
battery, more particularly to a lithium secondary battery which is
superior in safety and which has a high energy density.
BACKGROUND ART
[0002] In recent years, miniaturization and lightening have
acceleratively advanced in a notebook-size personal computer or a
portable electronic device selectively having functions of a
telephone, camera, GPS, radio, television and the like, and a
lithium secondary battery is preferably used.
[0003] The lithium secondary battery is a secondary battery in
which a lithium transition metal composite oxide is used in a
(cathode) active substance of a cathode plate, a carbonaceous
material is used in an (anode) active substance of an anode plate,
and a nonaqueous electrolytic solution obtained by dissolving a
lithium ion electrolyte in an organic solvent is used in an
electrolytic solution, respectively. The battery has a
characteristic that an energy density is large because an electric
cell voltage is about 4 V and high. Since the battery is
miniaturized and its voltage is raised owing to the characteristic
as compared with a conventional secondary battery, the battery is
not limited to the above-described application, the battery is also
noted as a power supply for driving a motor of an electric car or a
hybrid electric car that is positively and generally spreading as a
low-emission car in the background of a recent environmental
problem, and the application of the battery is enlarged more.
[0004] With the enlargement of the application, enhancement of
safety is required for the lithium secondary battery. Since the
lithium secondary battery having a high energy density and a large
capacity has a large absolute value of accumulated energy, a risk
in a case where the battery is improperly used is high. Therefore,
it is necessary to secure sufficient safety at a handling or
charging/discharging time.
[0005] According to the Battery Association of Japan, as an
improper use test of a safety evaluation standard guideline of the
lithium secondary battery, "nail sticking test" is specified in
which a metal rod is driven into an electrode member inside the
fully charged battery, and the cathode plate and the anode plate in
the electrode member are internally short-circuited. It is
determined that the safety should be secured without ignition,
explosion or the like of the battery even in a case where an
abnormal current rapidly flows. Moreover, to clear the nail
sticking test, as shown in FIG. 8, assuming a case where heat is
generated by the abnormal current, the electrolytic solution is
evaporated, and a battery inner pressure rises, the lithium
secondary battery 31 is provided with a pressure releasing
mechanism 32 which allows the release of the battery inner pressure
to an atmospheric air pressure (see, e.g., Patent Document 1).
[0006] Moreover, as shown in FIG. 9, a drop of battery performance
is sometimes caused unless gas purging is sufficiently secured in a
case where a gas is generated inside inner electrode members
(electrode structures 42). To solve the problem, there is disclosed
a lithium secondary battery 41 in which a plurality of
collector-foil-side pores 43 are made in a cathode-side collector
foil and an anode-side collector foil constituting the electrode
structures 42, a plurality of core-side pores 45 are also made in a
core 44 for taking up these collector foils, and the gas generated
in the electrode structures 42 are released by the
collector-foil-side pores 43 and the core-side pores 45 (see, e.g.,
Patent Document 2). It is to be noted that in FIG. 9, reference
numeral 46 denotes a battery case.
[0007] [Patent Document 1] Japanese Patent Application Laid-Open
No. 9-92249
[0008] [Patent Document 2] Japanese Patent Application Laid-Open
No. 10-162801
DISCLOSURE OF THE INVENTION
[0009] However, in the lithium secondary battery described in
Patent Document 1, there has been a problem that in a case where
the electrolytic solution is evaporated and gasified owing to the
heat generation by the abnormal current or the like, the gas is
easily accumulated inside the battery before reaching the pressure
releasing mechanism. Therefore, the gas cannot be sufficiently
purged through the operated pressure releasing mechanism, and it
sometimes becomes difficult to secure the safety of the
battery.
[0010] Moreover, the lithium secondary battery described in Patent
Document 2 has a problem that since the collector-foil-side pores
are made in the cathode-side collector foil and the anode-side
collector foil, the energy density of the inner electrode member
drops, and the capacity of the battery is reduced. Such lithium
secondary battery also has a problem that since the
collector-foil-side pores and the core-side pores need to be
positioned to manufacture the battery, manufacturing steps become
laborious, and costs increase.
[0011] The present invention has been developed in view of such
problems, and there is provided a lithium secondary battery in
which a gas generated inside an inner electrode member is prevented
from being accumulated inside the battery before reaching a
pressure releasing mechanism, and can be smoothly released and
which is superior in safety and which has a high energy
density.
[0012] That is, according to the present invention, there is
provided the following lithium secondary battery.
[0013] [1] A lithium secondary battery comprising:
[0014] an inner electrode member having wound or laminated
electrode plates of a metal foil; and
[0015] a battery case for housing the inner electrode member,
[0016] wherein when an inner pressure of the battery case rises to
a predetermined pressure or more by a gas generated inside the
inner electrode member, a gas release channel which allows the
release of the gas to the outside of the battery case is formed by
deformation of the inner electrode member by a raised inner
pressure.
[0017] [2] The lithium secondary battery according to the above
[1], wherein at least a part of the gas release channel is formed
inside the inner electrode member in a direction vertical to the
surface of the inner electrode member onto which the electrode
plate is wound or laminated.
[0018] [3] The lithium secondary battery according to the above
[2], wherein the deformation indicates that a pre-designed
predetermined portion of the metal foil is broken to form a
hole.
[0019] [4] The lithium secondary battery according to any one of
the above [1] to [3], wherein the inner electrode member further
has a core member onto which the electrode plate is wound or
laminated.
[0020] [5] The lithium secondary battery according to the above
[4], wherein the core member is shaped to have a predetermined
inner space and one or more through-holes formed to communicate
with the inner space, and the metal foil in the vicinity of the
through-hole is broken to form a hole, and the gas release channel
is formed which allows the release of the gas to the outside of the
battery case through the hole, the through-hole, and the inner
space by the function of the raised inner pressure when the inner
pressure rises to the predetermined pressure or more.
[0021] [6] The lithium secondary battery according to the above
[4], wherein the core member is provided with one or more groove
portions which extend to at least one end portion of the core
member, and the metal foil in the vicinity of the groove portion is
broken to form a hole, and the gas release channel is formed which
allows the release of the gas to the outside of the battery case
through the hole and the groove portion by the function of the
raised inner pressure in the case where the inner pressure rises to
the predetermined or more pressure.
[0022] [7] The lithium secondary battery according to the above
[4], wherein the core member is provided with two or more core
member elements having hollow portions and disposed in such a
manner that gap portions having predetermined intervals are formed
between the respective core member elements and the hollow portions
communicate with each other, and the metal foil in the vicinity of
the gap portion is broken to form a hole, and the gas release
channel is formed which allows the release of the gas to the
outside of the battery case through the hole, the gap portion, and
the hollow portions by the function of the raised inner pressure in
the case where the inner pressure rises to the predetermined or
more pressure.
[0023] [8] The lithium secondary battery according to the above
[3], further comprising: a first exterior member which is disposed
between the inner electrode member and the battery case and which
has a predetermined inner space and which is provided with one or
more through-holes which communicate with the inner space, wherein
the metal foil in the vicinity of the through-hole is broken to
form a hole, and the gas release channel is formed which allows the
release of the gas to the outside of the battery case through the
hole, the through-hole, and the inner space by the function of the
raised inner pressure when the inner pressure rises to the
predetermined pressure or more.
[0024] [9] The lithium secondary battery according to any one of
the above [3] to [8], wherein a strength (F1) of the battery case
and a strength (F2) of the portion of the metal foil material in
which the hole is formed satisfy a relation of F2<F1.
[0025] [10] The lithium secondary battery according to the above
[1], wherein the inner electrode member is expanded and deformed in
a thickness direction of the electrode plate, a space portion is
formed between the electrode plates disposed adjacent to each
other, and the gas release channel is formed which allows the
release of the gas to the outside of the battery case through the
space portion by the function of the raised inner pressure when the
inner pressure rises to the predetermined pressure or more.
[0026] [11] The lithium secondary battery according to the above
[10], further comprising: a second exterior member which is
disposed between the inner electrode member and the battery case
and which is deformable at a predetermined pressure, wherein the
second exterior member is deformed, and the inner electrode member
is expanded and deformed in a thickness direction of the electrode
plates by the function of the raised inner pressure when the inner
pressure rises to the predetermined pressure or more.
[0027] [12] The lithium secondary battery according to any one of
the above [1] to [11], wherein the battery case comprises a
pressure releasing mechanism, and an end of the gas release channel
communicates with the pressure releasing mechanism.
[0028] [13] The lithium secondary battery according to any one of
the above [1] to [12], wherein a shape of the core member is a
pipe-shape, and a whole shape is a cylindrical.
[0029] [14] The lithium secondary battery according to any one of
the above [1] to [12], wherein a shape of the core member is a
hollow plate-shape, and a whole shape of the battery is a
prismatic.
[0030] The lithium secondary battery of the present invention is
capable of smoothly releasing the pressure of the gas generated
inside the inner electrode member without retaining the gas before
the gas reaches the pressure releasing mechanism, and is remarkably
superior in safety. Since a substantial surface area of the metal
foil material constituting the cathode plate and the anode plate is
effectively utilized in the lithium secondary battery of the
present invention, the safety is enhanced while maintaining the
energy density to be high.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] [FIG. 1] A sectional view schematically showing one
embodiment of a lithium secondary battery of the present
invention;
[0032] [FIG. 2] An explanatory view schematically showing one
example of a core member for use in the lithium secondary battery
shown in FIG. 1, FIG. 2(a) is a front view viewed from a direction
vertical to a central axis, FIG. 2(b) is a side view viewed from a
direction parallel to the central axis, and FIG. 2(c) is a
sectional view of FIG. 2(a);
[0033] [FIG. 3] A perspective view showing one example of an inner
electrode member for use in the lithium secondary battery of the
present invention;
[0034] [FIG. 4] A perspective view showing another example of the
core member for use in the lithium secondary battery of the present
invention;
[0035] [FIG. 5] A perspective view showing another example of the
inner electrode member for use in the lithium secondary battery of
the present invention;
[0036] [FIG. 6] A sectional view schematically showing another
embodiment of the lithium secondary battery of the present
invention;
[0037] [FIG. 7] A perspective view showing one example of a
laminated inner electrode member for use in the lithium secondary
battery of the present invention;
[0038] [FIG. 8] A sectional view showing one embodiment of a
conventional lithium secondary battery;
[0039] [FIG. 9] An explanatory view showing another embodiment of
the conventional lithium secondary battery, FIG. 9(a) is a
perspective view, and FIG. 9(b) is a partially sectional view;
[0040] [FIG. 10] A perspective view showing still another example
of the core member for use in the lithium secondary battery of the
present invention;
[0041] [FIG. 11(a)] A perspective view showing a further example of
the core member for use in the lithium secondary battery of the
present invention;
[0042] [FIG. 11(b)] A partially sectional view showing a further
example of an inner electrode member for use in the lithium
secondary battery of the present invention;
[0043] [FIG. 12(a)] A perspective view showing a further example of
the core member for use in the lithium secondary battery of the
present invention;
[0044] [FIG. 12(b)] A partially sectional view showing a further
example of the inner electrode member for use in the lithium
secondary battery of the present invention;
[0045] [FIG. 13] A sectional view schematically showing still
another embodiment of the lithium secondary battery of the present
invention;
[0046] [FIG. 14] A sectional view schematically showing a further
embodiment of the lithium secondary battery of the present
invention;
[0047] [FIG. 15] A schematic diagram showing one example of a state
in which the inner electrode member is expanded and deformed in a
thickness direction of an electrode plate; and
[0048] [FIG. 16] A schematic diagram showing another embodiment of
the state in which the inner electrode member is expanded and
deformed in the thickness direction of the electrode plate.
DESCRIPTION OF REFERENCE NUMBERS
[0049] 1, 21, 31, 41, 93, 103, 123: lithium secondary battery, 2,
26: cathode plate, 3, 27: anode plate, 4, 24, 38, 44, 61, 71, 81:
core member, 6, 25, 37, 74, 85, 96, 106, 110, 126: inner electrode
member, 7, 28, 91, 101: through-hole, 8, 29, 62, 90, 100: inner
space, 9: pressure release hole, 10, 94, 104, 124: battery case,
11: separator, 12, 13: electrode lead wire, 14: electrode lid, 16:
cathode collector member, 17: anode collector member, 19: metal
foil, 20: pressure release valve, 32: pressure releasing mechanism,
33: cathode inner terminal, 34: anode inner terminal, 35: cathode
outer terminal, 36: anode outer terminal, 42: electrode structures,
43: collector-foil-side pores, 45: core-side pores, 51: necked
portion, 60: slit (notched portion), 70: groove portion, 72: end
portion, 73, 84, 95, 105, 111, 125: electrode plate, 80: core
member element, 82: gap portion, 83: hollow portion, 92: first
exterior member, 102: first exterior member, 112, 121: space
portion, 122: second exterior member, F1, F2: strength
BEST MODE FOR CARRYING OUT THE INVENTION
[0050] The best mode for carrying out the present invention will be
described hereinafter, but it should be understood that the present
invention is not limited to the following embodiment, and the scope
of the present invention includes appropriate modifications,
improvements and the like of the following embodiments based on
ordinary knowledge of a person skilled in the art without departing
from the scope of the present invention.
[0051] In one embodiment of the present invention, a lithium
secondary battery comprises: an inner electrode member having
electrode plates of a metal foil as a constituting element, and
being constituted by winding or laminating the electrode plates;
and a battery case for housing the inner electrode member. In the
lithium secondary battery of the present embodiment, a gas release
channel capable of releasing a gas to the outside of the battery
case is formed involving deformation of the inner electrode member
by a function of a raised inner pressure when the inner pressure of
the battery case rises to a predetermined pressure or more by means
of the gas generated inside the inner electrode member which is the
constituting element. Therefore, in the lithium secondary battery
of the present embodiment, the pressure inside the battery,
especially inside the inner electrode member does not easily
excessively rise even at an abnormal time, and breakage or ignition
by short-circuit of the battery case can be effectively
prevented.
[0052] Moreover, the lithium secondary battery of the present
embodiment does not have a configuration in which pores are made
beforehand in the electrode plate (metal foil material), and the
gas release channel is prepared beforehand as in the lithium
secondary battery described in, for example, Patent Document 2.
That is, the battery is constituted in such a manner that the inner
pressure which rises accompanying generation of abnormality is
utilized, and the gas release channel is formed by the function of
the raised inner pressure. Therefore, since it is not necessary to
perform beforehand such working as to reduce a surface area of the
electrode plate (metal foil material), for example, the making of
the pores, the battery has remarkably high energy density and
capacity.
[0053] Next, details of the gas release channel formed involving
the deformation of the inner electrode member will be described in
accordance with typical examples. Examples of a configuration in
which at least a part of the gas release channel is formed include:
a configuration in which the part of the gas release channel is
formed inside the inner electrode member in a direction vertical to
the surface of the inner electrode member onto which the electrode
plate is wound or laminated. Moreover, examples of the deformation
of the inner electrode member caused in this case include: (1) a
pre-designed predetermined portion of the metal foil material is
broken to form a hole; and (2) the inner electrode member is
expanded and deformed in the thickness direction of the electrode
plate.
[0054] It is to be noted that in the lithium secondary battery of
the present embodiment, the inner electrode member further has a
core member onto which the electrode plate is wound or laminated,
and this is preferable because it is possible to facilitate the
designing of the predetermined portion of the metal foil material
in which the hole is formed. More details of the lithium secondary
battery according to the present invention will be described
hereinafter specifically with reference to the drawings.
[0055] FIG. 1 is a sectional view schematically showing one
embodiment of the lithium secondary battery of the present
invention. FIG. 2 is an explanatory view schematically showing one
example of a core member for use in the lithium secondary battery
shown in FIG. 1, FIG. 2(a) is a front view viewed from a direction
vertical to a central axis, FIG. 2(b) is a side view viewed from a
direction parallel to the central axis, and FIG. 2(c) is a
sectional view of FIG. 2(a). As shown in FIGS. 1 and 2(a) to 2(c),
a lithium secondary battery 1 of the present embodiment comprises:
an inner electrode member 6 having electrode plates (cathode plates
2, anode plates 3) including metal foil materials as constituting
elements and constituted by winding or laminating the electrode
plates; and a battery case 10 containing this inner electrode
member 6. Here, in FIG. 1, reference numeral 16 denotes a cathode
collector member, 17 denotes an anode collector member, 33 denotes
a cathode inner terminal, 34 denotes an anode inner terminal, 35
denotes a cathode outer terminal, and 36 denotes an anode outer
terminal. It is to be noted that the inner electrode member 6 shown
in FIG. 1 is a wound type inner electrode member constituted by
winding the cathode plates 2 and the anode plates 3 around a core
member 4.
[0056] The core member 4 is shaped in such a manner as to have an
inner space 8 and at least one through-hole 7 which communicates
with the inner space 8. It is to be noted that at least one end
portion of this inner space 8 communicates with a pressure
releasing mechanism capable of releasing a gas generated inside the
inner electrode member 6 to the outside of the battery case 10.
Specifically, the end portion of the inner space 8 communicates
with a pressure release hole 9 (pressure release valve 20). In the
lithium secondary battery 1 of the present embodiment, first a
portion in the vicinity of the through-hole 7 of the metal foil
material is broken to form a hole (not shown) by a function of a
raised inner pressure when the inner pressure of the battery case
10 rises to a predetermined pressure or more by a gas generated
inside the inner electrode member 6. Accordingly, a gas release
channel is formed which is capable of releasing the generated gas
to the outside of the battery case 10 through the hole, the
through-hole 7, and the inner space 8. It is to be noted that when
the metal foil materials as the constituting elements of the
cathode plates 2 and the anode plates 3 are broken to form holes,
holes are simultaneously formed in separators 11 disposed in such a
manner as to prevent the cathode plates 2 from being brought into
contact with the anode plates 3.
[0057] In a conventional lithium secondary battery, a gap between
the electrode plates disposed adjacent to each other is utilized as
a release channel of a gas generated by an electrolytic solution
evaporated by heat generation attributable to an abnormal current.
Therefore, the gas is not satisfactorily released from the gap
between the adjacent electrode plates depending on an inner state
of the lithium secondary battery or an amount of the generated gas
in some case.
[0058] On the other hand, the lithium secondary battery 1 of the
present embodiment is constituted in such a manner that the
predetermined portion of the metal foil material is broken to form
the hole, and there is formed the gas release channel including
this hole, the through-hole 7, and the inner space 8 of the core
member 4 in the case where the inner pressure of the battery case
10 rises to the predetermined or more pressure by the gas generated
inside the inner electrode member 6. Therefore, when the gas is not
satisfactorily released from the gap between the adjacent electrode
plates (cathode plates 2, anode plates 3), and the inner pressure
rises, the above-described gas release channel is formed, and the
gas is released. Therefore, in the lithium secondary battery 1 of
the present embodiment, the pressure inside the battery, especially
inside the inner electrode member 6 does not easily excessively
rise even at an abnormal time, and breakage or ignition due to
short-circuit of the battery case 10 can be effectively
prevented.
[0059] Moreover, in the lithium secondary battery 1 of the present
embodiment, holes for pressure release do not have to be made
beforehand in the cathode plates 2 and the anode plates 3 which are
constituting members. Therefore, in the lithium secondary battery 1
of the present embodiment, the surface area of the metal foil
material is effectively utilized at a use time in a usual state,
and the energy density is remarkably high.
[0060] In the core member 4 for use in the lithium secondary
battery 1 shown in FIG. 1, 17 through-holes 7 are formed in an
axial direction of the core member, and four through-holes 7 are
formed in a peripheral direction, but in the lithium secondary
battery according to the present invention, there is not any
special restriction on the number, shape, size and the like of the
through-holes 7 formed in the core member 4 as long as an excessive
rise of the inner pressure is suppressed, and the gas can be
effectively released to the outside of the battery. Therefore, the
number and the like of the through-holes 7 formed in the core
member 4 may be appropriately set in accordance with a dimension of
the whole battery, materials or dimensions (thicknesses) of the
cathode plate 2, the anode plate 3, and the separator 11, a
pressure at which the release of the gas is initiated and the like.
A core member 61 having a shape shown in FIG. 10 can be used. The
core member 61 shown in FIG. 10 has an inner space 62, and is
provided with one or more slits (notched portions) 60 which
communicate with this inner space 62. That is, the "through-hole"
mentioned in the present specification conceptually includes the
slit (notched portion) 60 shown in FIG. 10. It is to be noted that
either of the through-hole and the slit (notched portion) may be
formed in the core member.
[0061] Moreover, FIG. 1 illustrates the core member 4 which is
cylindrical, and has a columnar whole shape in such a manner as to
guide the gas to the pressure release hole 9 via the through-holes
7, but the core member may be formed using a material provided with
a plurality of pores, such as a porous material. When the core
member is formed using such porous material or the like, the core
member does not have to be formed to be cylindrical, and the
generated gas can be guided into the pressure release hole 9 via
the pores in the porous material. It is to be noted that a metal
foil 19 and the pressure release valve 20 are disposed in the
pressure release hole 9, and the gas is released from this pressure
release valve 20 to thereby release the pressure.
[0062] FIG. 11(a) is a perspective view showing still another
example of the core member for use in the lithium secondary battery
of the present invention. In the lithium secondary battery
according to the present invention, as shown in FIG. 11(a), an
inner electrode member 74 (see FIG. 11(b)) is preferably
constituted using a core member 71 in which one or more groove
portions 70 are formed up to at least one end portion 72. When the
inner pressure of the lithium secondary battery according to the
present invention, which comprises the inner electrode member 74
shaped as shown in FIG. 11(b), rises to a predetermined pressure or
more, a portion of the metal foil constituting an electrode plate
73 is broken in the vicinity of the groove portion 70 to form a
hole (not shown). Accordingly, a gas release channel is formed
which allows the release of the generated gas to the outside of the
battery case through the holes and the groove portions 70, and an
effect similar to that of the lithium secondary battery 1 shown in
FIG. 1 can be obtained.
[0063] FIG. 12(a) is a perspective view showing still another
example of the core member for use in the lithium secondary battery
of the present invention. In the lithium secondary battery
according to the present invention, as shown in FIG. 12(a), gap
portions 82 having predetermined intervals are formed between two
or more core member elements 80 having hollow portions 83, and an
inner electrode member 85 (see FIG. 12(b)) is preferably
constituted using a core member 81 in which the hollow portions 83
are disposed in such a manner as to communicate with one another.
In a case where the inner pressure of the lithium secondary battery
according to the present invention, which comprises the inner
electrode member 85 shaped as shown in FIG. 12(b), rises to a
predetermined pressure or more, portions of the metal foil
constituting an electrode plate 84 are broken in the vicinity of
the gap portions 82 to form holes (not shown). Accordingly, a gas
release channel is formed which allows the release of the generated
gas to the outside of the battery case through the holes, the gap
portions 82, and the hollow portions 83, and an effect similar to
that of the lithium secondary battery 1 shown in FIG. 1 can be
obtained.
[0064] FIG. 13 is a sectional view schematically showing still
another embodiment of the lithium secondary battery of the present
invention, and shows the battery whose whole shape is columnar. A
lithium secondary battery 93 of the present embodiment has inner
spaces 90 between an inner electrode member 96 and a battery case
94, and further comprises a first exterior member 92 provided with
one or more through-holes 91 which communicate with this inner
spaces 90. It is to be noted that in the lithium secondary battery
93 of the present embodiment, a core member is not an indispensable
constituting element. In a case where the inner pressure of the
lithium secondary battery 93 according to the present invention
rises to a predetermined pressure or more, portions of a metal foil
material constituting an electrode plate 95 are broken in the
vicinity of the through-holes 91 to form holes (not shown).
Accordingly, a gas release channel is formed which allows the
release of the generated gas to the outside of the battery case
through the holes, the through-holes 91, and the inner spaces 90,
and an effect similar to that of the lithium secondary battery 1
shown in FIG. 1 can be obtained.
[0065] Moreover, FIG. 14 is a sectional view schematically showing
still another embodiment of the lithium secondary battery of the
present invention, and shows the battery whose whole shape is
prismatic. A lithium secondary battery 103 of the present
embodiment has an inner space 100 between an inner electrode member
106 and a battery case 104, and further comprises a first exterior
member 102 provided with one or more through-holes 101 which
communicate with this inner space 100. It is to be noted that in
the lithium secondary battery 103 of the present embodiment, a core
member is not an indispensable element. In a case where the inner
pressure of the lithium secondary battery 103 of the present
embodiment rises to a predetermined pressure or more, portions in
the vicinity of the through-holes 101 are broken to form holes (not
shown) in a metal foil material constituting an electrode plate
105. Accordingly, a gas release channel is formed which allows the
release of the generated gas to the outside of the battery case
through the holes, the through-holes 101, and the inner space 100,
and an effect similar to that of the lithium secondary battery 1
shown in FIG. 1 can be obtained.
[0066] FIG. 3 is a perspective view showing one example of an inner
electrode member for use in the lithium secondary battery of the
present invention. This inner electrode member 6 is a wound type
inner electrode member, and constituted by winding a cathode plate
2 and an anode plate 3 around an outer periphery of a core member
4. A separator 11 is disposed between the cathode plate 2 and the
anode plate 3. Therefore, the cathode plate 2 does not directly
contact the anode plate 3. Electrode lead wires 12, 13 for
performing electric connection are attached to the cathode plate 2
and the anode plate 3. At least one of each of the electrode lead
wires 12, 13 may be attached, but a plurality of electrode lead
wires 12, 13 may be attached to reduce a current collection
resistance.
[0067] The cathode plate 2 is constituted of a metal foil material
prepared by coating opposite surfaces of a collector substrate with
a cathode active substance. As the collector substrate, there is
used a metal foil such as an aluminum foil or a titanium foil
having a satisfactory corrosion resistance against a cathode
electrochemical reaction. It is to be noted that as the collector
substrate, a mesh (net) of a metal, a punching metal or the like
may be used. As the cathode active substance, a lithium transition
metal composite oxide is usable. It is to be noted that micro
carbon powder such as acetylene black is preferably added as an
auxiliary conductive agent to the lithium transition metal
composite oxide.
[0068] It is to be noted that as the lithium transition metal
composite oxide, in addition to lithium manganese (LiMnO.sub.4),
there may be used lithium nickel oxide (LiNiO.sub.2), lithium
cobalt oxide (LiCoO.sub.2), a manganese cobalt nickel composite
cathode material (LiMn.sub.1/3Co.sub.1/3Ni.sub.1/3O.sub.2) or the
like that has a thermal stability lower than that of lithium
manganese oxide (LiMnO.sub.4). In the lithium secondary battery
according to the present invention, not only in a case where
lithium manganese (LiMnO.sub.4) having a comparatively satisfactory
thermal stability is used as the cathode active substance but also
in a case where the above-described lithium transition metal
composite oxide having a lower thermal stability is used,
disadvantages such as breakage and ignition of the battery case are
not remarkably easily caused, and superior safety is secured.
[0069] The coating with the cathode active substance is performed
by coating the collector substrate with a slurry or a paste
prepared by adding a solvent, a bonding agent or the like to a
cathode active substance powder by use of a roll coater process or
the like, and drying the substrate. Thereafter, if necessary, a
pressing treatment or the like is performed.
[0070] The anode plate 3 can be prepared in the same manner as in
the cathode plate 2. As the metal foil material constituting the
anode plate 3, there is preferably used a metal foil such as a
copper foil or a nickel foil having a satisfactory corrosion
resistance against an anode electrochemical reaction as the
collector substrate. As an anode active substance, there is used an
amorphous carbonaceous material such as soft carbon or hard carbon,
or highly graphitized carbonaceous powder such as artificial
graphite or natural graphite.
[0071] The separator 11 is made of porous-polymer, cellulose or the
like. More typically, there is preferably used a three-layer
structure in which a polyethylene film (PE film) having micro pores
and permeable to lithium ions is sandwiched between porous
polypropylene films (PP films) permeable to the lithium ions. The
separator structured in this manner has a safety mechanism in a
case where a temperature of the inner electrode member rises, the
PE film softens at about 130.degree. C., the micro pores collapse,
and movement of the lithium ions, that is, a battery reaction is
inhibited. Since this PE film is sandwiched between the PP films
having a higher softening temperature, the PP films retain shapes
to prevent the cathode plate 2 from being brought into contact with
the anode plate 3 and prevent short-circuit therebetween even in a
case where the PE film softens. It is possible to securely inhibit
the battery reaction and secure the safety.
[0072] The electrode lead wires 12, 13 are attached to portions of
the cathode plate 2 and anode plate 3 in which the collector
substrate that is not coated with an electrode active substance is
exposed at a winding operation time for the cathode plate 2, the
anode plate 3, and the separator 11. As the electrode lead wires
12, 13, there are preferably used foil-like wires made of the same
materials as those of the collector substrates of the cathode plate
2 and the anode plate 3, respectively. The electrode lead wires 12,
13 can be attached to the cathode plate 2 and the anode plate 3 by
ultrasonic welding, spot welding or the like.
[0073] As a solvent for preparing a nonaqueous electrolytic
solution, there is preferably usable: carbonic acid ester such as
ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl
carbonate (DMC), or propylene carbonate (PC); or a single solvent
or a mixed solvent of .gamma.-butyrolactone, tetrahydrofuran,
acetonitrile or the like. Especially from viewpoints of
conductivity, high-temperature stability and the like of the
electrolytic solution, a mixed solvent of cyclic carbonate and
chain carbonate is preferably used.
[0074] Examples of an electrolyte for preparing the nonaqueous
electrolytic solution include: lithium complex fluorine compounds
such as lithium phosphate hexafluoride (LiPF.sub.6) and lithium
fluoroborate (LiBF.sub.4); and lithium halide such as lithium
perchlorate (LiClO.sub.4). One type or two or more types of them
can be dissolved in the above-described organic solvent (mixed
solvent) to thereby obtain the nonaqueous electrolytic solution. As
the electrolyte, LiPF.sub.6 is especially preferably used. This is
because oxidation decomposition does not easily occur, and
reliability is high.
[0075] Moreover, as shown in FIG. 1, the pressure release hole 9 as
the pressure releasing mechanism for use in the lithium secondary
battery 1 of the present embodiment is formed in a position
corresponding to a central portion of an electrode lid 14 in one
end surface of the lithium secondary battery 1. The core member 4
is disposed in central portion of the lithium secondary battery 1.
The pressure release hole 9 has such a structure that is integrated
with an outer terminal and does not hinder pressure release.
Therefore, the pressure releasing mechanism indicates satisfactory
pressure release operability although it has a simple constitution.
It is to be noted that the pressure releasing mechanism for use in
the lithium secondary battery according to the present invention is
not limited to the mechanism having the pressure release hole 9
shown in FIG. 1. That is, any conventional known pressure releasing
mechanism may be preferably adopted as long as the gas generated
inside the battery can be satisfactorily released.
[0076] It is to be noted that, as shown in FIG. 1, in the lithium
secondary battery 1 of the present embodiment, necked portions 51
are formed in the electrode lid 14 and/or a battery case 10 portion
right close to an outer edge portion of the electrode lid 14
provided with the pressure release hole 9, and this is preferable
because the electrode lid 14 is securely positioned and fixed. To
prepare the lithium secondary battery 1 having the pressure
releasing mechanism, first the necked portion 51 is formed in an
opening end portion of the battery case 10. Subsequently, a
plate-like member provided with a hole in a portion corresponding
to the pressure release hole 9 is welded and fixed to the opening
end portion of the battery case 10 in which the necked portion 51
is formed. Thereafter, a pressure release hole unit constituted
integrally with the pressure release hole 9 can be fitted into the
plate-like member to prepare the lithium secondary battery 1 having
the pressure releasing mechanism. When the necked portion 51 is
formed in the opening end portion of the battery case 10 in this
manner, a fitting stress generated in fitting the pressure release
hole unit into the plate-like member can be scattered in not only
the portion welded to the battery case 10 but also the necked
portion 51 of the battery case 10. Therefore, safety in production
is enhanced, and yield is also enhanced.
[0077] To assemble the lithium secondary battery 1 shown in FIG. 1,
the inner electrode member 6 is inserted into the battery case 10
to hold the member in a stable position while securing conduction
between a terminal for drawing a current to the outside and the
electrode lead wires 12, 13, and the battery is thereafter
impregnated with the nonaqueous electrolytic solution.
Subsequently, when the battery case 10 is sealed, the lithium
secondary battery 1 can be obtained. An oxidizing agent may be
preferably inserted into the battery case 10. When the oxidizing
agent for use is a gas such as air, oxygen, or ozone, the battery
may be assembled, and impregnated with the nonaqueous electrolytic
solution in an atmosphere including the gas.
[0078] It is to be noted that in the lithium secondary battery 1 of
the present embodiment, instead of attaching the electrode lead
wires 12, 13 to the cathode plate 2 and the anode plate 3
constituting the wound type inner electrode member 6, cathode
collector members may be welded and connected to a tip of a metal
foil material of the cathode plate 2, and an anode collector member
may be welded and connected to a tip of a metal foil material of
the anode plate 3, respectively, to form a so-called tab-less
structure type lithium secondary battery.
[0079] FIG. 1 shows the lithium secondary battery 1 in which the
shape of the core member 4 is cylindrical and whose whole shape is
columnar. In addition, for example, as shown in FIG. 4, a core
member 24 has a hollow plate shape, and a whole shape may be
prismatic. In a case where the core member 24 shaped in this manner
is used, as shown in FIG. 5, when an inner pressure rises to a
predetermined pressure or more, portions close to through-holes 28
(see FIG. 4) of the core member 24 are broken to form holes in the
metal foil materials constituting a cathode plate 26 and a anode
plate 27, a gas release channel is formed to extend through the
holes, the through-holes 28 (see FIG. 4) of the core member 24, and
an inner space 29, and a gas can be released to the outside of the
battery. Therefore, an effect similar to that of the lithium
secondary battery 1 shown in FIG. 1 can be obtained. FIG. 4 is a
perspective view showing another example of the core member for use
in the lithium secondary battery of the present invention, and FIG.
5 is a perspective view showing another example of the inner
electrode member for use in the lithium secondary battery of the
present invention. It is to be noted that in FIG. 5, reference
numeral 30 denotes a separator.
[0080] FIG. 6 is a sectional view schematically showing another
embodiment of the lithium secondary battery of the present
invention. A lithium secondary battery 21 of the present embodiment
shown in FIG. 6 comprises: an inner electrode member 6 having
electrode plates (cathode plates 2, anode plates 3) including metal
foil materials as constituting elements and constituted by winding
the electrode plates around a core member 4 via separators 11; and
a battery case 10 containing the inner electrode member 6. A
cathode collector member 16 and an anode collector member 17 for
deriving a current from the inner electrode member 6 are disposed.
It is to be noted that the core member 4 is provided with at least
one through-hole 7 which communicates with an inner space 8 of the
core member 4. The lithium secondary battery 21 of the present
embodiment is constituted in such a manner that a strength (F1) of
the battery case 10 and a strength (F2) of a portion (i.e., the
portion in which a hole is to be formed) close to the through-hole
7 of the metal foil material satisfy a relation F2<F1. The
lithium secondary battery 21 of the present embodiment comprises a
pressure release hole 9 as a pressure releasing mechanism, and the
through-holes 7 formed in the core member 4 and the inner space 8
which communicates with the through-holes 7 communicate with this
pressure release hole 9.
[0081] In the lithium secondary battery 21 of the present
embodiment, when an inner pressure of a battery case 10 rises to a
predetermined pressure or more, portions of the metal foil
constituting the electrode plates (cathode plate 2, anode plate 3)
close to the through-holes 7 of the core member 4 are broken to
form holes. Here, since the lithium secondary battery 21 of the
present embodiment is constituted in such a manner as to satisfy
the relation of F2<F1, the holes are formed in a stage in which
the battery case 10 is broken. Therefore, the gas release channel
extending through the formed holes, the through-holes 7, and the
inner space 8 is formed before the battery case 10 breaks, and the
generated gas is guided into the pressure release hole 9.
Therefore, the battery is remarkably superior in safety.
[0082] Moreover, the lithium secondary battery according to the
present invention is preferably constituted in such a manner that,
as shown in FIG. 15, when an inner pressure rises to a
predetermined pressure or more, by a function of the raised inner
pressure, an inner electrode member 110 is expanded and deformed in
a thickness direction of electrode plates 111, space portions 112
are formed between the electrode plates 111 disposed adjacent to
each other, and a gas release channel is formed that is capable of
releasing a gas generated inside the inner electrode member to the
outside of the battery case through the formed space portions 112.
In this case, a main portion of the gas release channel is formed
in parallel with a surface wound with (or laminated on) the
electrode plate 111 between the adjacent electrode plates 111, and
an effect similar to the lithium secondary battery 1 shown in FIG.
1 can be obtained.
[0083] Furthermore, as shown in FIG. 16, the lithium secondary
battery according to the present invention further comprises a
second exterior member 122 which is deformable at a predetermined
pressure between an inner electrode member 126 and a battery case.
The battery is preferably constituted in such a manner that in a
case where an inner pressure rises to the predetermined or more
pressure, by the function of the raised inner pressure, the second
exterior member 122 is deformed, and the inner electrode member 126
is expanded and deformed in a thickness direction of an electrode
plate 125. In a lithium secondary battery 123 of the present
embodiment constituted in this manner, when the inner electrode
member 126 is expanded and deformed, space portions 121 are formed
between the electrode plates 125 disposed adjacent to each other,
and a gas release channel is formed that is capable of releasing a
gas generated inside the inner electrode member 126 to the outside
of a battery case 124 through the formed space portions 121.
Therefore, an effect similar to that of the lithium secondary
battery 1 shown in FIG. 1 can be obtained.
[0084] It is to be noted that the "function of the inner pressure"
includes a function of an inner temperature which rises with the
rise of the inner pressure. Therefore, the second exterior member
122 softens by the temperature rise, or is sometimes molten and
deformed. There is not any special restriction on a material
constituting the second exterior member 122 as long as the material
is deformed, softened, or molten at an appropriate pressure or
temperature, and a thermoplastic resin material or the like can be
preferably used.
[0085] The embodiments of the lithium secondary battery of the
present invention have been described above in accordance with the
example in which the wound type inner electrode member is mainly
used, but, needless to say, the lithium secondary battery of the
present invention is not limited to the above-described
embodiments. There may be used, for example, a laminated type inner
electrode member 37 comprising a core member 38 shown in FIG. 7.
The lithium secondary battery according to the present invention is
especially preferably adopted in a large-sized battery having a
battery capacity of 2 Ah or more, but there is not any restriction
on application to a battery having more capacity. The lithium
secondary battery of the present invention is also preferable as a
car-mounted battery of an electric vehicle (EV), a hybrid electric
vehicle (HEV) or the like, or a motor driving power supply for an
EV, HEV or the like by use of a characteristic that the battery has
a large capacity at a reduced cost, and a high reliability, and is
superior in long-term storage. Furthermore, the battery is also
preferable as a power supply for starting an engine, for which a
high output is required.
[0086] As described above, the lithium secondary battery of the
present invention is constituted in such a manner that in a case
where the inner pressure rises to the predetermined or more
pressure by the gas generated inside the inner electrode member
constituting the battery, the gas release channel is formed
involving the deformation of the inner electrode member by the
function of the raised inner pressure. Therefore, the substantial
surface areas of the metal foil materials constituting the cathode
plate and the anode plate are effectively utilized, the energy
density is maintained to be high, and the battery has a remarkably
superior safety.
EXAMPLE
[0087] The present invention will be described hereinafter in more
detail in accordance with examples, but the present invention is
not limited to the examples.
Example 1
[0088] To lithium manganese (Li was excessive, and a part of Mn was
replaced with Ti in a composition represented by LiMn.sub.2O.sub.4)
spinel used as a cathode active substance, 4% by mass of acetylene
black in terms of an external ratio was added as an auxiliary
conductive agent, and further a solvent and a binder were added to
prepare a cathode slurry. Opposite surfaces of an aluminum foil
having a thickness of 20 .mu.m were coated with the slurry in such
a manner as to achieve a thickness of about 50 .mu.m, and a cathode
plate having a thickness of about 120 .mu.m was prepared.
[0089] On the other hand, opposite surfaces of a copper foil having
a thickness of 10 .mu.m were coated with an anode slurry prepared
by use of graphite as an anode active substance in such a manner as
to achieve a thickness of about 40 .mu.m, and an anode plate having
a thickness of about 90 .mu.m was prepared.
[0090] The prepared cathode plate and anode plate were wound, via a
separator (PP/PE/PP (three layers)), around a core member provided
with at least one hole and constituted in such a manner that in a
case where a pressure inside a lithium secondary batter rose to a
predetermined pressure or more, a gas was released from a hole made
by the broken cathode plate, anode plate or the like to thereby
prepare a wound type inner electrode member. On the other hand,
various types of organic solvents such as EC, DMC, and DEC were
mixed at a volume ratio of 1:1:1 to prepare a mixed solvent,
LiPF.sub.6 as an electrolyte was dissolved in the solvent in such a
manner as to obtain a concentration of 1 mol/l, and a nonaqueous
electrolytic solution was prepared.
[0091] An aluminum-made cylindrical battery case in which the wound
type inner electrode member was stored was charged with the
nonaqueous electrolytic solution, and the battery case was sealed
to thereby prepare a lithium secondary battery (provided with a
pressure release valve) having a cell capacity of 5 Ah (Example 1).
It is to be noted that the battery was prepared all by a dry
process, and this eliminated an influence of a water content or the
like that might enter from the outside of the battery owing to a
sealing defect of the battery case.
[0092] Next, after the resultant lithium secondary battery (Example
1) was fully charged, an overcharging test was performed in which
constant current charging (maximum voltage of a constant current
power supply 200 A was set to 18 V) was continued.
Example 2
[0093] A lithium secondary battery Example 2 was manufactured by a
method similar to that of Example 1 except that lithium nickel
oxide (a part of Ni was replaced with Co and Al in a composition
represented by LiNiO.sub.2) spinel was used as a cathode active
substance. Furthermore, an overcharging test was conducted in the
same manner as in Example 1.
Comparative Example 1
[0094] A lithium secondary battery (Comparative Example 1) was
manufactured by a method similar to that of Example 1 except that a
conventional core member in which any hole was not formed was used
as a core member to prepare a wound type inner electrode member.
Furthermore, an overcharging test was conducted in the same manner
as in Example 1.
Comparative Example 2
[0095] A lithium secondary battery (Comparative Example 2) was
manufactured by a method similar to that of Example 2 except that a
conventional core member in which any hole was not formed was used
as a core member to prepare a wound type inner electrode member.
Furthermore, an overcharging test was conducted in the same manner
as in Example 1.
[0096] In the lithium secondary batteries of Examples 1 and 2, a
metal foil material close to the core member was broken along the
hole formed in the core member, and the pressure was released from
this hole of the core member through a space in the core member
owing to a rise of an inner pressure at an overcharging time.
Therefore, the wound type inner electrode member wound with the
metal foil material was not extremely broken, the battery case was
not broken by the pressure rise, and the batteries were superior in
safety.
[0097] On the other hand, in the lithium secondary battery of
Comparative Example 1, at the overcharging time, the pressure
release in the wound type inner electrode member did not catch up
with the rise of the inner pressure, and the wound type inner
electrode member was ruptured inside the battery case owing to the
pressure rise. Furthermore, in the lithium secondary battery of
Comparative Example 2, it was observed that the battery case was
broken and ignited. This is supposedly because in the lithium
secondary battery of Comparative Example 2, there was used lithium
nickel oxide having a thermal stability lower than that of lithium
manganese used in the lithium secondary battery of Comparative
Example 1.
[0098] According to the above-described result, it has been found
that superior safety can be secured even in a case where there is
used, as the cathode active substance, lithium nickel oxide having
a thermal stability lower that that of lithium manganese (i.e.,
reactivity is higher at an improper use test such as the
overcharging test). It is to be noted that when the lithium
secondary battery was manufactured by a method similar to that of
Example 1 by use of lithium cobalt oxide (LiCoO.sub.2) or a
manganese cobalt nickel composite cathode material
(LiMn.sub.1/3Co.sub.1/3Ni.sub.1/3O.sub.2) that has a thermal
stability lower than that of lithium manganese oxide, in addition
to the above-described cathode active substance. Moreover, the
overcharging test was performed. In this case, a superior safety
similar to that of the lithium secondary battery of Example 1 or 2
could be confirmed.
INDUSTRIAL APPLICABILITY
[0099] A lithium secondary battery of the present invention can be
preferably used in a motor driving battery for an electric car or a
hybrid electric car.
* * * * *